Semiconductor memory device with memory cells having same characteristics and manufacturing method for the same

ABSTRACT

In a method of manufacturing a semiconductor memory device, a lower electrode film is formed on a semiconductor substrate via an interlayer insulating film. A ferroelectric film is formed on the lower electrode layer while heating the lower electrode layer uniformly in the cell array region. An upper electrode film is formed on the ferroelectric film. Ferroelectric capacitors are formed in a memory cell array region. Each of the ferroelectric capacitors includes the lower electrode film, the ferroelectric film and the upper electrode film.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor memory devicewhich has a ferroelectric capacitor. More particularly, the presentinvention relates to the technique for achieving uniform operationcharacteristics over the whole of a memory cell array region of thesemiconductor memory device.

[0003] 2. Description of the Related Art

[0004] A semiconductor memory device which has a ferroelectric capacitoris conventionally known. An example of such a conventional semiconductormemory device will be described using a logic circuit embedded FeRAM(Ferroelectric Random Access Memory). FIG. 1 shows an example of thecircuit layout of a macro of the logic circuit embedded FeRAM.

[0005] Referring to FIG. 1, the macro of the logic circuit embeddedFeRAM has a plurality of memory cell arrays. Sense amplifiers arearranged to sandwich each memory cell array in a horizontal direction,and word line and plate line drivers are arranged to sandwich a set ofthe sense amplifiers and the memory cell arrays in a vertical direction.Moreover, an X decoder is arranged above the uppermost word line andplate line driver. A Y decoder is arranged on the left side of the setsof the sense amplifiers and the memory cell arrays. A space is providedbetween the memory cell array and the sense amplifier and between thememory cell array and the word line and plate line driver. The space ishereinafter called a “connection region”.

[0006]FIG. 2 shows a circuit diagram of FeRAM cells of the memory cellarray. As shown in FIG. 2 as a unit cell of 2T2C, the FeRAM cell iscomprised of two transistors and two ferroelectric capacitors. The FeRAMcell with the structure of 2T2C holds data by applying two voltages ofdifferent polarities to the ferroelectric capacitors. In case of readingthe data, plate lines are biased from a ground voltage to a power supplyvoltage and the electric charge from the ferroelectric capacitor withthe polarity inverted and the electric charge from the ferroelectriccapacitor with the polarity non-inverted are outputted onto a pair ofbit lines. Then, the voltage difference on the pair of bit lines isamplified by the sense amplifier and outputted outside.

[0007]FIG. 3 shows a cross sectional view of the conventional logiccircuit embedded FeRAM formed as mentioned above. The logic circuitembedded FeRAM has a 3-layer wiring line structure. The logic circuitembedded FeRAM has a memory cell array region where the FeRAM cells arearranged, a peripheral circuit region where peripheral circuits such asthe sense amplifier, the word line driver and the plate line driver arearranged, and a connection region formed between them.

[0008] In the memory cell array region, the ferroelectric capacitor iscomprised of an upper electrode, a ferroelectric film and a lowerelectrode and is formed on an uppermost aluminum wiring line layercontaining third metal wiring lines. In the connection region, a dummycapacitor shown by slanted lines is comprised of the upper electrode,the ferroelectric film and the lower electrode. The dummy capacitorfunctions to prevent 2-dimension effects such as proximity effect andpattern sparse dense effect in a lithography process or a dry etchingprocess in the connection region so that the ferroelectric capacitorsare formed to have a predetermined size over the whole of the memorycell array region.

[0009] By the way, the logic circuit embedded FeRAM has theferroelectric capacitors on an aluminum wiring line layer, as describedabove, and a contact plug is comprised of tungsten. The aluminum wiringline layer is damaged when annealing is carried out in a hightemperature (600° C. to 750° C.) to form the ferroelectric capacitor.Therefore, a crystal growth method is conventionally adopted to form theferroelectric capacitor at a relatively low temperature. In this case,it is essential to form the ferroelectric capacitor at the growthtemperature of 450° C. or below to maintain the reliability of thecontact plug and the aluminum wiring line. Generally, when the growthtemperature of a PZT (Pb(Zr_(x),Ti_(1−x))O₃) film as a ferroelectricfilm is lowered, the crystalline of the PZT film is degraded and theferroelectric characteristics are degraded.

[0010] The characteristic 1 (solid line) in FIG. 4 shows theferroelectric characteristics when the PZT film is formed at the growthtemperature of 450° C. In this case, the ferroelectric capacitor withlarge polarization can be formed. Also, the characteristic 2 (brokenline) shows the ferroelectric characteristics when the PZT film isformed at the growth temperature of 430° C. In the case, theferroelectric capacitor with small polarization is formed.

[0011]FIG. 5 is a diagram showing the bit line voltage difference of allthe FeRAM cells of a test memory cell array which contains the cells forvoltage measurement. In FIG. 5, the bit line voltage difference from 0 Vto about 1.3 V is shown in a sparse dense manner of dots. A part of adarker color shows a larger bit line voltage difference. Each of theFeRAM cells has the PZT film manufactured at the growth temperature of430° C. The FeRAM cell has a larger bit line voltage difference or alarger operation margin when the bit line voltage difference is larger.Referring to FIG. 5, the operation margin of the FeRAM cell is large ina right end section and in the center section and the operation marginof the FeRAM cell is small in an upper end section and a lower endsection. The operation margin depends on the characteristics of theferroelectric capacitor, as shown in FIG. 4. That is, the operationmargin is large when the polarization is large like the characteristic1, and the operation margin is small when the polarization is small likethe characteristic 2.

[0012] The deviation in the operation margin depending on the physicalposition of the FeRAM cell results from the difference in thecharacteristics of the FeRAM cells, as shown in FIG. 5. It could beconsidered that the deviation is based on the surface temperature of thelower electrode, which is generally comprised of platinum (Pt), of theferroelectric capacitor when the PZT film is formed.

[0013] In conjunction with the above description, a semiconductor memorydevice is disclosed in Japanese Laid Open Patent Application(JP-A-Heisei 4-168765). In this reference, the memory device iscomprised of a memory cell array region where a plurality of memorycells are formed, each of which is comprised of a memory transistor anda capacitor, and a peripheral circuit region where a plurality ofperipheral circuit transistors are formed. The memory device is formedon a semiconductor substrate. A set of gate electrode films is arrangedin parallel in the memory cell array region to have a predeterminedspace. Thus, using the gate electrodes, memory transistors are formed. Aset of gate electrode films is arranged in parallel in the peripheralcircuit region to have a predetermined space. Thus, using the gateelectrodes, peripheral circuit transistors are formed. Dummy wiringlines are also formed in the peripheral circuit region. The spacebetween the gate electrodes films in the memory cell array region issubstantially the same as the space between the gate electrodes films orbetween the gate electrode and the dummy wiring line in the memory cellarray region.

[0014] Also, a semiconductor device is disclosed in is disclosed inJapanese Laid Open Patent Application (JP-A-Heisei 11-74482). In thereference, a plurality of semiconductor devices are formed on asemiconductor substrate in a memory cell region to have conductive filmspiled via insulating films. A dummy pattern has at least a conductivefilm and is formed on a position closer to the peripheral transistorregion than any one of the semiconductor devices. An interlayerinsulating film covers the semiconductor devices and the dummy patternand has an inclined portion between the memory cell region and theperipheral transistor region. A part of the dummy pattern is exposedfrom the interlayer insulating film.

SUMMARY OF THE INVENTION

[0015] Therefore, an object of the present invention is to provide asemiconductor memory device and a manufacturing method, in which memorycells with large operation margins can be formed over the whole of amemory cell array region.

[0016] In an aspect of the present invention, a method of manufacturinga semiconductor memory device is achieved by (a) forming a lowerelectrode film on a semiconductor substrate via an interlayer insulatingfilm; by (b) forming a ferroelectric film on the lower electrode layerwhile heating the lower electrode layer; by (c) forming an upperelectrode film on the ferroelectric film; and by (d) formingferroelectric capacitors in a memory cell array region, each of theferroelectric capacitors comprising the lower electrode film, theferroelectric film and the upper electrode film.

[0017] Here, it is desirable that the lower electrode film is formed ofmaterial containing at least one of platinum, iridium, iridium oxide,ruthenium and ruthenium oxide.

[0018] Also, the method may further comprise the step of (e) formingthermally conductive routes in the memory cell array region and aconnection region outside the memory cell array region to pass throughthe interlayer insulating film to the semiconductor substrate, and to beconnected with the lower electrode film. The lower electrode film isheated via the thermally conductive routes. In this case, it isdesirable that contact plugs for the routes passing through a portion ofthe interlayer insulating film are formed each time the interlayerinsulating film portion is formed. Also, the heating may be achieved byheating the semiconductor substrate.

[0019] Also, it is desirable that a density of the thermally conductiveroutes in the memory cell array region is substantially the same as thatof the thermally conductive routes in the connection region

[0020] Also, additional thermally conductive routes may be formed in theinterlayer insulating film in a peripheral circuit region outside theconnection region to be connected with the thermally conductive routesin the connection region.

[0021] Also, the (b) forming step may desirably include heating thesemiconductor substrate to about 450° C.

[0022] Also, the (a) forming step may be achieved by forming the lowerelectrode film to extend outside the memory cell array region.

[0023] In another aspect of the present invention, a semiconductormemory device having a memory cell array region, a peripheral circuitregion and a connection region between the memory cell array region andthe peripheral circuit region, includes ferroelectric capacitors formedon a semiconductor substrate via an interlayer insulating film in thememory cell array region; and conductive films formed on the interlayerinsulating film in the connection region. The conductive films areconnected with the semiconductor substrate via conductive routes passingthrough the interlayer insulating film, respectively.

[0024] Here, a layer for the conductive films may be formed when a lowerelectrode layer for the ferroelectric capacitors is formed. In thiscase, the lower electrode layer may be formed of material containing atleast one of platinum, iridium, iridium oxide, ruthenium and rutheniumoxide.

[0025] Also, the semiconductor memory device may further include MOStransistors formed on the semiconductor substrate in the memory cellarray region and the connection region. Each of the ferroelectriccapacitors may be connected with one of the MOS transistors formed inthe memory cell array region and each of the conductive films may beconnected with one of the MOS transistors formed in the connectionregion.

[0026] Also, it is desirable that a density of the ferroelectriccapacitors is substantially the same as that of the conductive films.

[0027] Also, the semiconductor memory device may further includeadditional conductive films formed in the peripheral circuit region. Theadditional conductive films may be connected with any of the conductiveroutes in the connection region.

[0028] The semiconductor memory device may be a logic circuit embeddedFeRAM, or a logic circuit embedded non-volatile SRAM.

[0029] In another aspect of the present invention, a method ofmanufacturing a semiconductor memory device, may be achieved by (a)forming MOS transistors in a memory cell array region and a connectionregion outside the memory cell array region, wherein a density of theMOS transistors in the memory cell array region is substantially thesame as that of the MOS transistors in the connection region; by (b)forming an interlayer insulating film to cover the MOS transistors whileforming thermally conductive routes, each of which extends from one ofthe MOS transistors to pass through the interlayer insulating film; by(c) forming a lower electrode film on a semiconductor substrate via theinterlayer insulating film to be connected with the thermally conductiveroutes; by (d) forming a ferroelectric film on the lower electrode layerwhile heating the lower electrode layer; by (e) forming an upperelectrode film on the ferroelectric film; and by (f) formingferroelectric capacitors in the memory cell array region, each of theferroelectric capacitors comprising the lower electrode film, theferroelectric film and the upper electrode film.

[0030] In another aspect of the present invention, a method ofmanufacturing a semiconductor memory device, may be achieved by (a)forming MOS transistors in a memory cell array region and a connectionregion outside the memory cell array region, wherein a density of theMOS transistors in the memory cell array region is substantially thesame as that of the MOS transistors in the connection region; by (b)forming an interlayer insulating film to cover the MOS transistors whileforming thermally conductive routes, each of which extends from one ofthe MOS transistors to pass through the interlayer insulating film; by(c) forming a lower electrode film on a semiconductor substrate via theinterlayer insulating film to be connected with the thermally conductiveroutes; by (d) forming a ferroelectric film on the lower electrode layerwhile heating the lower electrode layer via the thermally conductiveroutes; by (e) forming an upper electrode film on the ferroelectricfilm; and by (f) forming ferroelectric capacitors in the memory cellarray region, each of the ferroelectric capacitors comprising the lowerelectrode film, the ferroelectric film and the upper electrode film.

[0031] Here, the (b) forming step further may be achieved by formingadditional thermally conductive routes in the interlayer insulating filmin a peripheral circuit region outside the connection region to beconnected with the thermally conductive routes in the connection region.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a circuit diagram showing the circuit layout of atypical logic circuit embedded FeRAM;

[0033]FIG. 2 is a circuit diagram of a typical FeRAM cell of the logiccircuit embedded FeRAM;

[0034]FIG. 3 is a cross sectional view of a conventional logic circuitembedded FeRAM;

[0035]FIG. 4 is a diagram showing the difference in the ferroelectriccharacteristics depending on the forming temperature of a ferroelectricfilm;

[0036]FIG. 5 is a diagram showing a bit line voltage difference in allthe FeRAM cells of a memory cell array in the conventional logic circuitembedded FeRAM;

[0037]FIG. 6 is a cross sectional view of a logic circuit embedded FeRAMaccording to a first embodiment of the present invention;

[0038]FIGS. 7A to 7G are cross sectional views showing a manufacturingprocess of the logic circuit embedded FeRAM according to the firstembodiment of the present invention;

[0039]FIG. 8 is a diagram showing the circuit layout of a logic circuitembedded non-volatile SRAM according to a second embodiment of thepresent invention;

[0040]FIG. 9 is a circuit diagram showing an SRAM cell of the logiccircuit embedded non-volatile SRAM according to the second embodiment ofthe present invention;

[0041]FIG. 10 is a cross sectional view showing the logic circuitembedded non-volatile SRAM according to the second embodiment of thepresent invention; and

[0042]FIGS. 11A to 11H are cross sectional views showing a manufacturingprocess of the logic circuit embedded non-volatile SRAM according to thesecond embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Hereinafter, a semiconductor memory device and a manufacturingmethod for the same of the present invention will be described in detailwith reference to the attached drawings.

[0044] (Embodiment 1)

[0045] The semiconductor memory device according to the first embodimentof the present invention relate to a logic circuit embedded FeRAM.

[0046] The semiconductor memory device according to the first embodimentof the present invention has the same circuit layout as that of theconventional logic circuit embedded FeRAM shown in FIG. 1. That is, thelogic circuit embedded FeRAM macro has a plurality of memory cellarrays. Sense amplifiers are arranged to sandwich each memory cell arrayin a horizontal direction, and sets of a word line driver and a plateline driver are arranged to sandwich a set of the two memory cell arraysand the three sense amplifiers. Moreover, an X decoder is arranged abovethe top of the sets of the word line driver and the plate line driver. AY decoder is arranged on the left side of the three sets of the wordline driver and the plate line driver and the two sets of the two memorycell arrays and the three sense amplifiers. Thus, a connection region isformed between the memory cell array and the sense amplifier and betweenthe memory cell array and the set of the word line driver and the plateline driver.

[0047] The semiconductor memory device according to the first embodimentof the present invention has the same circuit as the FeRAM cell shown inFIG. 2. That is, as shown in FIG. 2 as a unit cell of 2T2C, the FeRAMcell is comprised of two transistors and two ferroelectric capacitors.In the FeRAM cell with the structure of 2T2C, voltages of differentpolarities are applied to the two ferroelectric capacitors to storedata. When the data is read out, the voltage of the plate line isincreased from the ground voltage to a power supply voltage. At thistime, the electric charge of the capacitor with the polarity invertedand the electric charge of the capacitor with the polarity non-invertedare transferred onto a pair of bit lines. The voltage difference on thebit lines is amplified by a sense amplifier and outputted.

[0048]FIG. 6 shows a cross sectional view of the logic circuit embeddedFeRAM according to the first embodiment of the present invention formedas mentioned above. The logic circuit embedded FeRAM has a 3-layerwiring line structure. Also, the logic circuit embedded FeRAM has amemory cell array region where the FeRAM cells are arranged, aperipheral circuit region where peripheral circuits such as the senseamplifier, the word line driver and the plate line driver are arranged,and a connection region which is formed between the memory cell arrayregion and the peripheral circuit region.

[0049] In the memory cell array region, a ferroelectric capacitor 70 iscomprised of a lower electrode 61, a ferroelectric film 62 and an upperelectrode 63, and is formed on the uppermost wiring line layer as awiring line 50, which is necessary for the peripheral circuit region.Also, dummy capacitors 70 a and 70 b are formed in the connection regionto have the same structure as the ferroelectric capacitor 70. Moreover,dummy capacitors 70 c and 70 d are formed in a part of the peripheralcircuit region to have the same structure as the ferroelectric capacitor70.

[0050] The lower electrode 61 of each of the dummy capacitors 70 a, 70b, 70 c and 70 d is thermally connected to a silicon substrate 10through a “heat transfer route” which comprised of a lower electrodecontact plug 51, a third wiring line 50, a third contact plug 41, asecond wiring line 40, a second contact plug 31, a first wiring line 30and a first contact plug 21. Thus, the heat transfer route transfersheat from the silicon substrate 10 to the lower electrode 61.

[0051] Next, a manufacturing method will be described with reference tocross sectional views of FIGS. 7A to 7G showing each manufacturingprocess of the logic circuit embedded FeRAM according to the firstembodiment of the present invention.

[0052] First, as shown in FIG. 7A, CMOS transistors are formed on asilicon substrate 10. That is, a P-well 11 and an N-well 12 are formedin the silicon substrate 10 and an element isolation region 13 is formedbetween the connection region and the peripheral circuit region. Next, agate insulating film (not shown) and gate electrodes 20 are formed inthe memory cell array region, the connection region and the peripheralcircuit region. Then, n-type diffusion layers 14 are formed for the gateelectrodes 20 in the P-well 11 and p-type diffusion layers 15 are formedfor the gate electrodes 20 in the N-well 12, by the well-known method.Thus, the CMOS transistors are completed. In this case, the gateelectrode 20 a is formed in the connection region as a dummy gateelectrode.

[0053] Next, as shown in FIG. 7B, an first interlayer insulating film 22is formed and first contact plugs 21 are formed to extend to thediffusion layers of the CMOS transistors. The first wiring lines 30 areformed to be connected with the first contact plugs 21. For example, thefirst contact plug 21 is comprised of tungsten and connects the CMOStransistor and the first wiring line 30. The first contact plugs 21 aand 21 b are formed in the connection region, and are dummy contactplugs provided to thermally connect the silicon substrate 10 and thefirst wiring line 30. The interlayer insulating film 22 is comprised ofa silicon oxide film as a main component to cover the CMOS transistor.The first wiring line 30 is comprised of aluminum and connects betweenelements formed in the FeRAM. The first wiring lines 30 a and 30 b areformed in the connection region, and are dummy wiring lines provided totransfer heat.

[0054] Next, as shown in FIG. 7C, a second interlayer insulating film 32and a second contact plug 31 are formed to cover the first wiring lines30. Second contact plugs 31 are formed in the second interlayerinsulating film 32 to be connected with the first wiring lines 30. Then,second wiring lines 40 are formed on the second interlayer insulatingfilm 32. The second contact plug 31 is comprised of tungsten andconnects a corresponding one of the first wiring lines 30 and acorresponding one of the second wiring lines 40. The second contactplugs 31 a and 31 b are formed in the connection region as dummy contactplugs provided to thermally connect the first wiring line 30 and thesecond wiring line 40. The second interlayer insulating film 32 iscomprised of a silicon oxide film to cover the first wiring lines 30.The second wiring line 40 is comprised of aluminum and connects elementsformed in the FeRAM. The second wiring lines 40 a, 40 b, 40 c, 40 d, 40e and 40 f are dummy wiring lines are provided to transfer heat. Any ofthe second wiring lines 40 a, 40 b, 40 c and 40 d formed in theconnection region are connected directly or via the silicon substratewith the second wiring lines 40 e and 40 f formed in the peripheralcircuit region.

[0055] Next, as shown in FIG. 7D, a third interlayer insulating film 42is formed to cover the second wiring lines, and third contact plugs 41are formed in the third interlayer insulating film 42 to be connectedwith the second wiring lines 40 which are connected with the secondcontact plugs 31. Then, third wiring lines 50 are formed on the thirdinterlayer insulating film 42. The third contact plug 41 is comprised oftungsten and connects a corresponding one of the second wiring lines 40and a corresponding one of the third wiring lines 50. The third contactplugs 41 a and 41 b formed in the connection region are dummy contactplugs provided to thermally connect the second wiring lines 40 and thethird wiring lines 50. The third interlayer insulating film 42 iscomprised of a silicon oxide film and insulates between the secondwiring line 40 and the third wiring line 50. The third wiring line 50 iscomprised of aluminum and connects between the elements formed in theFeRAM. The third wiring lines 50 a, 50 b, 50 c and 50 d are dummy wiringlines to transfer heat. The third wiring line 50 d extends to theperipheral circuit region. Any of the third wiring lines 50 a, 50 b, and50 c formed in the connection region are connected directly or via thesilicon substrate 10 with the third wiring line 50 d in the peripheralcircuit region.

[0056] Next, as shown in FIG. 7E, a fourth interlayer insulating film 52is formed to cover the third wiring lines, and lower electrode contactplugs 51 are formed in the fourth interlayer insulating film 52. Then, astacked layer 60 of Pt/TiN/Ti for the lower electrode 61 of aferroelectric capacitor 70 is formed on the fourth interlayer insulatingfilm 52. The lower electrode contact plugs 51 are comprised of tungstenand connect corresponding ones of the third wiring lines 50 and thestacked layer 60. The lower electrode contact plugs 51 a and 51 b in theconnection region and the lower electrode contact plugs 51 c and 51 d inthe peripheral circuit region are dummy contact plugs provided tothermally connect the third wiring line 50 and the stacked layer 60. Thelower electrode contact plugs 51 a and 511 b formed in the connectionregion are connected directly or indirectly with the lower electrodecontact plugs 51 c and 51 d formed in the peripheral circuit region. Thefourth interlayer insulating film 52 is comprised of a silicon oxidefilm and insulates between the third wiring line 50 and the stackedlayer 60. As the material of the stacked layer 60, Pt, Ir and the oxide(e.g., IrO₂), Ru and the oxide (e.g., RuO₂), the stacked film ofIr/Ti/TiN/Ti, the stacked layer of SrRuO₃/Pt/TiN/Ti and so on can beused other than the above stacked layer 60.

[0057] Subsequently, while the substrate 10 is heated from the backsideof the silicon substrate 10 in the state that the above stacked layer 60is formed, a PZT layer for ferroelectric films is deposited on thestacked layer 60. Elements such as La and Ca may be added to the PZTfilm by a small amount for the purpose to improve reliability. The heatapplied from the side of the silicon substrate 10 is transferred via theheat transfer route comprised of the first contact plug 21, the firstwiring line 30, the second contact plug 31, the second wiring line 40,the third contact plug 41, the third wiring line 50 and the lowerelectrode contact plug 51 to the Pt/TiN/Ti stacked film 60 in the memorycell array region, the connection region and the peripheral circuitregion.

[0058] By the way, the heat transfer routes formed in the memory cellarray region and the connection region have an approximately uniformdensity over the memory cell array region and the connection region.Therefore, the whole of the memory cell array region can be heatedapproximately uniformly. In this way, the peripheral portion of thememory cell array region never remains low in temperature, unlike theconventional example. As a result, the ferroelectric layer excellent inthe ferroelectric characteristics can be formed in the whole of thememory cell array region. It should be noted that the density of theheat transfer route is not uniform in the peripheral circuit region.Therefore, because the surface temperature decreases from the connectionregion to the peripheral circuit region, the ferroelectric layer isformed to be inferior in ferroelectric characteristics. However, becausethe ferroelectric capacitors formed in the connection region and theperipheral circuit region are the dummy capacitors, no influence givesthe performance of the FeRAM cell.

[0059] Next, as shown in FIG. 7F, an upper electrode layer is formed onthe ferroelectric layer, and then is patterned. Thus, the upperelectrodes 63 are formed. The upper electrodes 63 may be comprised of astacked film of TiN/Ir, a stacked film of TiN/Al/TiN, and a stacked filmof Pt/SrRuO₃. Then, the PZT layer is patterned to produce theferroelectric films 62. Subsequently, the stacked layer 60 is patternedusing the PZT films 62 to produce the lower electrodes 61. Thus, theferroelectric capacitors 70 are formed, as shown in FIG. 7G. Theferroelectric capacitors 70 a, 70 b, 70 c and 70 d formed in theconnection region and the peripheral circuit region are dummy capacitorsto provided to transfer the heat.

[0060] Next, as shown in FIG. 6, an interlayer insulating film 71 isformed cover the ferroelectric capacitors. Then, upper electrodecontacts 71 are formed in the interlayer insulating film 71 on the upperelectrode 63. Subsequently, a plate line contact 72 is formed in theperipheral circuit region. Thereafter, a plate line layer is formed onthe interlayer insulating film 71 and patterned. Thus, the plate linesare formed. The upper electrode contact 71 is comprised of tungsten, andconnects a corresponding one of the ferroelectric capacitors 70 and acorresponding one of the plate lines which are connected with the plateline driver (see FIG. 2). The plate lines 80 a, 80 b, 80 c and 80 dformed in the connection region and the peripheral circuit region aredummy plate lines.

[0061] As described above, according to the logic circuit embedded FeRAMaccording to the first embodiment of the present invention, the heattransfer route is provided in the connection region formed between thememory cell array region and the peripheral circuit region to havesubstantially the same structure as the memory cell array region. Whenthe PZT film 62 is deposited as the ferroelectric film 62, the heat istransferred from the silicon substrate 10 to the stacked film 60 ofPt/TiN/Ti as the lower electrode. Therefore, the memory cell arrayregion is heated approximately uniformly, and the peripheral portion ofthe memory cell array region is never remained in a low temperature,unlike the conventional device. As a result, the PZT film superior inthe ferroelectric characteristics can be formed in the memory cell arrayregion.

[0062] It should be noted that in the above-mentioned first embodiment,the heat transfer route is formed in a part of the connection region andperipheral circuit region. However, after the ferroelectric capacitor 70is formed, the heat transfer route is unnecessary. Therefore, theprocess for removing the above heat transfer route after forming theferroelectric capacitor 70 may be provided.

[0063] Also, in the above-mentioned first embodiment, the dummycapacitors are formed in the connection region and the peripheralcircuit region. Also, the upper electrode contact 71 and the plate line80 are formed to be connected with the upper electrode of the dummycapacitor. However, like the second embodiment to be described later,only the lower electrode of the dummy capacitor is formed in theconnection region and the peripheral circuit region, and the process offorming of the upper electrode 63 and the process of forming the upperelectrode contact and the plate line can be omitted.

[0064] Moreover, in the above-mentioned first embodiment, theferroelectric capacitor 70 is formed above the uppermost third wiringline layer. However, the position where the ferroelectric capacitor 70is formed is not limited to the above position in the present inventionand is optional.

[0065] (Embodiment 2)

[0066] The semiconductor memory device and the manufacturing methodaccording to the second embodiment of the present invention relate tothe logic circuit embedded non-volatile SRAM and the manufacturingmethod.

[0067]FIG. 8 shows an example of the circuit layout of the logic circuitembedded non-volatile SRAM according to the second embodiment of thepresent invention. The logic circuit embedded non-volatile SRAM has aplurality of memory cell arrays. Sense amplifiers are arranged tosandwich each memory cell array in the vertical direction. A word linedriver is arranged on the left side of the memory cell arrays and thesense amplifiers and a plate line driver is arranged on the right sideof the memory cell arrays and the sense amplifiers. Moreover, a decoderis arranged on the left side of the word line driver. An input/output(I/O) circuit is arranged on the lower end side of the lowest senseamplifier. A connection region is formed between the memory cell arrayand the sense amplifier, between the memory cell array and the word linedriver between the memory cell array and the plate line driver.

[0068]FIG. 9 shows a circuit diagram of the nonvolatile SRAM cell of theabove memory cell array. The non-volatile SRAM cell contains sixtransistors and two ferroelectric capacitors. Because the structure andoperation of the non-volatile SRAM cell are well known, the descriptionabout them is omitted.

[0069]FIG. 10 shows a cross sectional view of the logic circuit embeddednon-volatile SRAM according to the second embodiment of the presentinvention. The logic circuit embedded non-volatile SRAM has a 4-layerwiring line structure, and is comprised of a memory cell array regionwhere SRAM cells are arranged, a peripheral circuit region whereperipheral circuits such as the sense amplifier, the word line driverand the plate line driver are arranged, and the connection region formedbetween the memory cell array region and the peripheral circuit region.

[0070] In the memory cell array region, the ferroelectric capacitor 70is comprised of a lower electrode 61, a ferroelectric film 62 and anupper electrode 63, and is formed on the uppermost wiring line. Also, inthe connection region, only the lower electrodes 61 a and 61 b of dummycapacitors are formed to have the same structure as the ferroelectriccapacitor 70. Moreover, the lower electrodes 61 c and 61 d of the dummycapacitors are formed in a part of the peripheral circuit region. Thelower electrodes 61 a, 61 b, 61 c and 61 d of the dummy capacitorscorrespond to the dummy electrodes of the present invention.

[0071] Each of the lower electrodes 61 a, 61 b, 61 c and 61 d isthermally connected to a silicon substrate 10 through a “heat transferroute” comprised of the lower electrode contact plug 51, a fourth wiringline 90, a fourth contact plug 81, a third wiring line 50, a thirdcontact plug 41, a second wiring line 40, a second contact plug 31, afirst wiring line 30 and a first contact plug.

[0072] Next, a manufacturing method of the logic circuit embeddednon-volatile SRAM according to the second embodiment of the presentinvention will be described with reference to the cross sectional viewsof FIGS. 11A to 11H.

[0073] At first, as shown in FIG. 11A, CMOS transistors are formed onthe silicon substrate 10. That is, P-wells 11 and N-wells 12 are formedin the silicon substrate 10. Then, an element isolation region 13 isformed. Subsequently, a gate insulating film (not shown) and the gateelectrodes 20 are formed on the substrate 10. Thereafter, n-typediffusion layers 14 and p-type diffusion layers 15 are formed by thewell-known method using the gate electrodes. Thus, the CMOS transistorsare formed. Now, the gate electrodes 20 a, 20 b, and 20 c formed in theconnection region and the gate electrode 20 d formed in the peripheralcircuit region are dummy gate electrodes.

[0074] Next, as shown in FIG. 11B, a first interlayer insulating film 22is formed to cover the CMOS transistors. Subsequently, first contactplugs 21 are formed in the first interlayer insulating film 22 to reachthe CMOS transistors. Then, a first wiring line layer is formed on thefirst interlayer insulating film 22 and patterned. Thus, first wiringlines 30 are formed. The first contact plug 21 is comprised of tungstenand connects a corresponding one of the CMOS transistors and acorresponding one of the first wiring lines 30. The first contact plugs21 a, 21 b, 21 c and 21 d formed in the connection region are dummycontact plugs provided to thermally connect the silicon substrate 10 andthe first wiring line 30. Also, the first interlayer insulating film 22is comprised of a silicon oxide film and insulates between the CMOStransistors and the first wiring lines 30. The first wiring line 30 iscomprised of aluminum and connects between elements which are formed inthe non-volatile SRAM. The first wiring lines 30 a, 30 b, 30 c and 30 dformed in the connection region are dummy wiring lines provided totransfer heat.

[0075] Next, as shown in FIG. 11C, a second interlayer insulating film32 is formed to cover the first wiring lines 30. Subsequently, secondcontact plugs 31 are formed in the second interlayer insulating film 32to reach the first wiring lines 30. Then, a second wiring line layer isformed on the second interlayer insulating film 32 and patterned. Thus,the second wiring lines 40 are formed. The second contact plug 31 iscomprised of tungsten and connects a corresponding one of the firstwiring lines 30 and a corresponding one of the second wiring lines 40.The second contact plugs 31 a, 31 b and 31 c formed in the connectionregion and the second contact plugs 31 d formed in the peripheralcircuit region are dummy contact plugs provided to thermally connect thefirst wiring lines 30 and the second wiring lines 40. Also, the secondinterlayer insulating film 32 is comprised of a silicon oxide film andinsulates between the first wiring lines 30 and the second wiring lines40. The second wiring line 40 is comprised of aluminum and connectsbetween elements formed in the non-volatile SRAM. The second wiringlines 40 a, 40 b and 40 c formed in the connection region and the secondwiring line 40 d formed in the peripheral circuit region are dummywiring lines provided to transfer heat.

[0076] Next, as shown in FIG. 11D, a third interlayer insulating film 42is formed to cover the second wiring lines 40. Subsequently, thirdcontact plugs 41 are formed in the third interlayer insulating film 42to reach the second wiring lines 40. Then, a third wiring line layer isformed on the third interlayer insulating film 42 and is patterned.Thus, the third wiring lines 50 are formed. The third contact plug 41 iscomprised of tungsten and connects a corresponding one of the secondwiring lines 40 and a corresponding one of the third wiring lines 50.The third contact plugs 41 a, 41 b and 41 c formed in the connectionregion are dummy contact plugs provided to thermally connect the secondwiring line 40 and the third wiring line 50. Also, the third interlayerinsulating film 42 is comprised of a silicon oxide film and insulatesbetween the second wiring line 40 and the third wiring line 50. Thethird wiring line 50 is comprised of aluminum and connects betweenelements formed in the non-volatile SRAM. The third wiring lines 50 a,50 b, 50 c and 50 d in the connection region and the third wiring line50 e formed in the peripheral circuit region are dummy wiring linesprovided to transfer heat. The third wiring lines 50 a, 50 b, 50 c and50 d in the connection region are connected directly or indirectly withthe third wiring line 50 e.

[0077] Next, as shown in FIG. 11E, a fourth interlayer insulating film82 is formed to cover the third wiring lines, and then fourth contactplugs 81 are formed in the fourth interlayer insulating film 82 to reachthe third wiring lines 50. Then, a fourth wiring line layer is formed onthe fourth interlayer insulating film 82 and is patterned. Thus, thefourth wiring lines 90 are formed. The fourth contact plug 81 iscomprised of tungsten and connects a corresponding one of the thirdwiring line 50 and a corresponding one of the fourth wiring line 90. Thefourth contact plugs 81 a and 81 b formed in the connection region aredummy contact plugs provided to thermally connect the third wiring line50 and the fourth wiring line 90. Also, the fourth interlayer insulatingfilm 82 is comprised of a silicon oxide film and insulates between thethird wiring lines 50 and the fourth wiring lines 90. The fourth wiringline 90 is comprised of aluminum and connects between elements formed inthe non-volatile SRAM. The fourth wiring lines 90 a, 90 b and 90 cformed in the connection region and the fourth wiring line 90 dextending from the connection region to the peripheral circuit regionare dummy wiring lines provided to transfer heat. The fourth wiringlines 90 a, 90 b and 90 c are connected directly or indirectly with thefourth wiring line 90 d.

[0078] Next, as shown in FIG. 11F, a fifth interlayer insulating film 52is formed to cover the fourth wiring lines 90, and then lower electrodecontact plugs 51 are formed in the fifth interlayer insulating film 52to reach the fourth wiring lines 90. Subsequently, a stacked layer 60 ofRu/Ti/TiN/Ti for the lower electrode 61 of the ferroelectric capacitor70 is formed on the fifth interlayer insulating film 52. The lowerelectrode contact plug 51 is comprised of tungsten and connects acorresponding one of the fourth wiring line 90 and the stacked film 60.The lower electrode contact plugs 51 a and 51 b formed in the connectionregion and the lower electrode contact plugs 51 c and 51 d formed in theperipheral circuit region are dummy contact plugs provided to thermallyconnect the fourth wiring line 90 and the stacked film 60. The lowerelectrode contact plugs 51 a and 51 b are connected directly orindirectly with the lower electrode contact plugs 51 c and 51 d. Also,the fifth interlayer insulating film 52 is comprised of a silicon oxidefilm and insulates between the fourth wiring lines 90 and the stackedfilm 60. As the material of the stacked film 60, Pt, Ir and the oxide(e.g., IrO2), Ru and the oxide (e.g., RuO2), the stacked film ofIr/Ti/TiN/Ti, the stacked film of SrRuO3/Pt/TiN/Ti and so on can be usedother than the above materials.

[0079] Subsequently, in the state in which the above stacked film 60 isformed, the PZT layer for the ferroelectric films is deposited while thewhole silicon substrate is heated to the temperature of 410° C. from theside of the silicon substrate 10. The film thickness of the PZT layerformed is 250 nm. In this case, the heat applied from the side of thesilicon substrate 10 is transferred to the stacked layer 60 ofRu/Ti/TiN/Ti in the memory cell array region, the connection region andthe peripheral circuit region via the heat transfer route comprised ofthe first contact plug 21, the first wiring line 30, the second contactplug 31, the second wiring line 40, the third contact plug 41, the thirdwiring line 50, the fourth contact plug 81, the fourth wiring line 90and the lower electrode contact plug 51.

[0080] Now, because the heat transfer routes are formed in the memorycell array region and the connection region to have a substantiallyuniform density, the memory cell array region is heated almostuniformly, and the peripheral section of the memory cell array regionnever remain low in temperature, unlike the conventional example. As aresult, the PZT layer superior in the ferroelectric characteristics canbe formed in the memory cell array region. It should be noted that thedensity of the heat transfer route is not uniform in the peripheralcircuit region, compared with the memory cell array region and theconnection region. Therefore, because the heat inclination is generatedfrom the connection region to the peripheral circuit region, the PZTlayer inferior in the ferroelectric characteristics is formed. However,the ferroelectric capacitors formed in these regions are dummycapacitors, and there is no influence in the performance of the SRAMcell.

[0081] Next, as shown in FIG. 11G, the upper electrode layer is formedon the PZT layer in the memory cell array region. Then, the upperelectrode layer is patterned to produce the upper electrodes 63. In thiscase, no upper electrode is formed in the connection region and theperipheral circuit region. The upper electrode 63 can be composed of thestacked film of TiN/Ru.

[0082] Next, as shown in FIG. 13, the PZT layer is patterned. Thus, theferroelectric films 62 are formed on the lower electrode layer 60.Subsequently, the lower electrode layer 60 is patterned using theferroelectric films 62. Thus, the lower electrodes 61 are formed. Inthis way, the ferroelectric capacitors 70 are formed in the memory cellarray region. Portions 61 a, 61 b, 61 c and 61 d corresponding to thelower electrodes 61 of the ferroelectric capacitor 70 are left as thedummy electrode in the connection region and the peripheral circuitregion.

[0083] Next, as shown in FIG. 10, an interlayer insulating film isformed to cover the ferroelectric capacitors 70. Subsequently, upperelectrode contacts 71 are formed in the interlayer insulating film toreach the upper electrodes 63 in the memory cell array region. Also, aplate line contact 72 is formed in the interlayer insulating film in theperipheral circuit region. Then, a plate line layer is formed on theinterlayer insulating film and patterned. Thus, plate lines 80 areformed. The upper electrode contact 71 is comprised of tungsten andconnects the ferroelectric capacitor 70 and the plate line driver (seeFIG. 8) via the plate line. In case of the nonvolatile SRAM, any dummyplate line contact and plate line are not formed.

[0084] As described above, according to the logic circuit embeddednon-volatile SRAM according to the second embodiment of the presentinvention, the heat transfer route having the same structure as in thememory cell array region is formed in the connection region between thememory cell array region and the peripheral circuit region. When the PZTlayer is deposited for the ferroelectric film 62 on the stacked film 60,the heat is transferred from the silicon substrate 10 to the stackedfilm 60. Therefore, the memory cell array region is heated uniformly andthere is no case that the peripheral section of the memory cell arrayregion remains low in temperature, unlike the conventional example. As aresult, in the memory cell array region, the PZT film is formed to beexcellent in the ferroelectric characteristics.

[0085] It should be noted that in the above-mentioned second embodiment,the heat transfer route is formed in the connection region and theperipheral circuit region. However, after the ferroelectric capacitorsare formed, the heat transfer route is unnecessary. Therefore, theprocess to remove the above heat transfer route may be provided afterforming the ferroelectric capacitor.

[0086] Also, in the above-mentioned second embodiment, the lowerelectrode as the dummy electrode of the dummy capacitor is formed in theconnection region and the peripheral circuit region, but the upperelectrode 63, the upper electrode contact and the plate line are notformed. However, the dummy capacitor may be formed in the connectionregion and the peripheral circuit region like the above-mentioned firstembodiment. Also, the upper electrode contact 71 and the plate line 80may be formed to be connected with the upper electrode of the dummycapacitor.

[0087] Moreover, in the above-mentioned second embodiment, theferroelectric capacitor is formed on the fourth wiring line as theuppermost layer. However, in the present invention, the position wherethe ferroelectric capacitor 70 is formed is not limited to the aboveposition and may be optional.

[0088] As described above, according to the present invention, there areprovided the semiconductor memory device and the manufacturing method inwhich the memory cells with a large operation margin are formed over thewhole region of the memory cell array.

What is claimed is:
 1. A method of manufacturing a semiconductor memorydevice, comprising the steps of: (a) forming a lower electrode film on asemiconductor substrate via an interlayer insulating film; (b) forming aferroelectric film on said lower electrode layer while heating saidlower electrode layer; (c) forming an upper electrode film on saidferroelectric film; and (d) forming ferroelectric capacitors in a memorycell array region, each of said ferroelectric capacitors comprising saidlower electrode film, said ferroelectric film and said upper electrodefilm.
 2. The method according to claim 1, wherein said lower electrodefilm is formed of material containing at least one of platinum, iridium,iridium oxide, ruthenium and ruthenium oxide.
 3. The method according toclaim 1, further comprising the step of: (e) forming thermallyconductive routes in said memory cell array region and a connectionregion outside said memory cell array region to pass through saidinterlayer insulating film to said semiconductor substrate, and to beconnected with said lower electrode film, and wherein said (b) formingstep comprises the step of: heating said lower electrode film via saidthermally conductive routes.
 4. The method according to claim 3, whereinsaid (e) forming step of: forming contact plugs for said routes passingthrough a portion of said interlayer insulating film each time saidinterlayer insulating film portion is formed.
 5. The method according toclaim 3, wherein said heating comprises the step of: heating saidsemiconductor substrate.
 6. The method according to claim 3, wherein adensity of said thermally conductive routes in said memory cell arrayregion is substantially the same as that of said thermally conductiveroutes in said connection region
 7. The method according to claim 3,wherein said (e) forming step further comprises the step of: formingadditional thermally conductive routes in said interlayer insulatingfilm in a peripheral circuit region outside said connection region to beconnected with said thermally conductive routes in said connectionregion.
 8. The method according to claim 1, wherein said (b) formingstep comprises the step of: heating said semiconductor substrate toabout 450° C.
 9. The method according to claim 1, wherein said (a)forming step comprises the step of: forming said lower electrode film toextend outside said memory cell array region.
 10. A semiconductor memorydevice having a memory cell array region, a peripheral circuit regionand a connection region between said memory cell array region and saidperipheral circuit region, comprising: ferroelectric capacitors formedon a semiconductor substrate via an interlayer insulating film in saidmemory cell array region; and conductive films formed on said interlayerinsulating film in said connection region, and wherein said conductivefilms are connected with said semiconductor substrate via conductiveroutes passing through said interlayer insulating film, respectively.11. The semiconductor memory device according to claim 10, wherein alayer for said conductive films is formed when a lower electrode layerfor said ferroelectric capacitors is formed.
 12. The semiconductormemory device according to claim 11, wherein said lower electrode layeris formed of material containing at least one of platinum, iridium,iridium oxide, ruthenium and ruthenium oxide.
 13. The semiconductormemory device according to claim 10, further comprising MOS transistorsformed on said semiconductor substrate in said memory cell array regionand said connection region, and wherein each of said ferroelectriccapacitors is connected with one of said MOS transistors formed in saidmemory cell array region and each of said conductive films is connectedwith one of said MOS transistors formed in said connection region. 14.The semiconductor memory device according to claim 10, wherein a densityof said ferroelectric capacitors is substantially the same as that ofsaid conductive films.
 15. The semiconductor memory device according toclaim 10, further comprising additional conductive films formed in saidperipheral circuit region, and wherein said additional conductive filmsare connected with any of said conductive routes in said connectionregion.
 16. The semiconductor memory device according to claim 10,wherein said semiconductor memory device is a logic circuit embeddedFeRAM.
 17. The semiconductor memory device according to claim 10,wherein said semiconductor memory device is a logic circuit embeddednon-volatile SRAM.
 18. A method of manufacturing a semiconductor memorydevice, comprising the steps of: (a) forming MOS transistors in a memorycell array region and a connection region outside said memory cell arrayregion, wherein a density of said MOS transistors in said memory cellarray region is substantially the same as that of said MOS transistorsin said connection region; (b) forming an interlayer insulating film tocover said MOS transistors while forming thermally conductive routes,each of which extends from one of said MOS transistors to pass throughsaid interlayer insulating film; (c) forming a lower electrode film on asemiconductor substrate via said interlayer insulating film to beconnected with said thermally conductive routes; (d) forming aferroelectric film on said lower electrode layer while heating saidlower electrode layer; (e) forming an upper electrode film on saidferroelectric film; and (f) forming ferroelectric capacitors in saidmemory cell array region, each of said ferroelectric capacitorscomprising said lower electrode film, said ferroelectric film and saidupper electrode film.
 19. A method of manufacturing a semiconductormemory device, comprising the steps of: (a) forming MOS transistors in amemory cell array region and a connection region outside said memorycell array region, wherein a density of said MOS transistors in saidmemory cell array region is substantially the same as that of said MOStransistors in said connection region; (b) forming an interlayerinsulating film to cover said MOS transistors while forming thermallyconductive routes, each of which extends from one of said MOStransistors to pass through said interlayer insulating film; (c) forminga lower electrode film on a semiconductor substrate via said interlayerinsulating film to be connected with said thermally conductive routes;(d) forming a ferroelectric film on said lower electrode layer whileheating said lower electrode layer via said thermally conductive routeson a side of said semiconductor substrate; (e) forming an upperelectrode film on said ferroelectric film; and (f) forming ferroelectriccapacitors in said memory cell array region, each of said ferroelectriccapacitors comprising said lower electrode film, said ferroelectric filmand said upper electrode film.
 20. The method according to claim 19,wherein said (b) forming step further comprises the step of: formingadditional thermally conductive routes in said interlayer insulatingfilm in a peripheral circuit region outside said connection region to beconnected with said thermally conductive routes in said connectionregion.